1. Field of the Invention
This invention is directed generally to the field of lightning arresters for protecting electrical signal lines against voltage surges and, more specifically, to an improved compact construction of a failsafe lightning arrester which can protect a plurality of lines.
2. Description of the Prior Art
An article titled "New Gas Tube Protector Technique for Circuits" by C. Bruce Barksdale appeared in TELEPHONY Oct. 17, 1970 and describes in detail the more commonly used means of protecting electrical lines against induced lightning surges. Briefly, this article described the use of a gas filled discharge tube containing three electrodes, one of the electrodes is grounded and the other two electrodes are connected to signal lines, such as two-wire telephone lines. Types of suitable gas-filled discharge tubes and their manner of construction and operation is described in U.S. Pat. Nos. 3,522,570 and 3,535,779 by Wanaselja. Basically, a high voltage electrical impulse such as that induced on telephone lines by nearby lightning, if of a magnitude that equals the ignition or firing threshold of the gas tube, causes the gas in the tube to ionize and, thereby, provide a low resistance electrical path to ground for both lines. This prevents the high surge from reaching the equipment being fed by the signal lines, such as a telephone receiver and transmitter. With telephone lines, both lines are simultaneously grounded through the tube because all of the electrodes are located in a single cavity so that once the gas in the cavity ionizes, it provides a low resistance path to ground for all of the electrodes.
A U.S. Pat. No. 3,816,802 issued to Crask and Egerer describes gas filled discharge tubes containing step-up transformers for protecting signal lines.
One of the problems with existing lightning arresters is that they are usually very bulky and are for protection of two or less lines. The present invention, in contrast, provides a cylindrical housing with an insulating seal and a plurality of electrodes to protect against surge voltages on up to four lines and yet is substantially smaller than existing devices to enable the arrester to be conveniently installed in areas where there is little space.